Granular polysilicon, such as chemical vapor deposition grown fluidized bed granular polysilicon, is typically delivered to a crystal growing facility in a shipping container. A conventional container has 300 kg of granular polysilicon. The granular polysilicon is typically sized between 400 and 1400 microns, and any particles sized less than 10 microns is considered dust. As a practical matter, all containers include some amount of dust therein.
When the granular polysilicon is transferred from the container to a feeder system of a crystal grower, the dust is also transferred to the feeder system. From the feeder system, the dust can settle and collect on the surface of the crystal grower hot zone, especially on colder surfaces in advanced “closed” crystal growers. The dust may then contact the crystal or the silicon melt near the crystal/melt interface. Such contact significantly increases the risk of undesirable defects, such as “Loss of Zero Dislocation” (LZD) in high quality semiconductor crystal. Such crystal and the advanced grower used to grow the crystal are found to be “dust sensitive.”
While relatively small batches of prior art granular polysilicon have included acceptably low amounts of dust, there has been no reliable system for obtaining such low-dust polysilicon in large quantities and using modern continuous manufacturing methods. Accordingly, improved methods of and apparatus for reducing the dust in the granular polysilicon are needed.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.